mark scheme (results) january 2019 - pmt

Mark Scheme (Results)

January 2019 Pearson Edexcel International

Advanced Subsidiary Level

In Chemistry (WCH11)

Paper 01 Structure, Bonding and Introduction

to Organic Chemistry

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January 2019

Publications Code WCH11_01_1901_MS

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General Marking Guidance

All candidates must receive the same treatment. Examiners

must mark the first candidate in exactly the same way as they mark the

last.

Mark schemes should be applied positively. Candidates must be

rewarded for what they have shown they can do rather than penalised

for omissions.

Examiners should mark according to the mark scheme not

according to their perception of where the grade boundaries may lie.

There is no ceiling on achievement. All marks on the mark

scheme should be used appropriately.

All the marks on the mark scheme are designed to be awarded.

Examiners should always award full marks if deserved, i.e. if the answer

matches the mark scheme. Examiners should also be prepared to award

zero marks if the candidate’s response is not worthy of credit according

to the mark scheme.

Where some judgement is required, mark schemes will provide the

principles by which marks will be awarded and exemplification may be

limited.

When examiners are in doubt regarding the application of the

mark scheme to a candidate’s response, the team leader must be

consulted.

Crossed out work should be marked UNLESS the candidate has

replaced it with an alternative response.

Using the Mark Scheme

Examiners should look for qualities to reward rather than faults to penalise. This does

NOT mean giving credit for incorrect or inadequate answers, but it does mean allowing

candidates to be rewarded for answers showing correct application of principles and

knowledge. Examiners should therefore read carefully and consider every response: even

if it is not what is expected it may be worthy of credit.

The mark scheme gives examiners:

an idea of the types of response expected

how individual marks are to be awarded

the total mark for each question

examples of responses that should NOT receive credit.

/ means that the responses are alternatives and either answer should receive full

credit.

( ) means that a phrase/word is not essential for the award of the mark, but helps the

examiner to get the sense of the expected answer.

Phrases/words in bold indicate that the meaning of the phrase or the actual word is

essential to the answer.

ecf/TE/cq (error carried forward) means that a wrong answer given in an earlier part of a

question is used correctly in answer to a later part of the same question.

Candidates must make their meaning clear to the examiner to gain the mark. Make sure

that the answer makes sense. Do not give credit for correct words/phrases which are put

together in a meaningless manner. Answers must be in the correct context.

Quality of Written Communication

Questions which involve the writing of continuous prose will expect candidates to:

write legibly, with accurate use of spelling, grammar and punctuation in order to make

the meaning clear

select and use a form and style of writing appropriate to purpose and to complex

subject matter

organise information clearly and coherently, using specialist vocabulary when

appropriate.

Full marks will be awarded if the candidate has demonstrated the above abilities.

Questions where QWC is likely to be particularly important are indicated (QWC) in the

mark scheme, but this does not preclude others.

Section A (Multiple Choice)

Question

number

Answer Mark

1

The only correct answer is B (8 neutrons and 10 electrons)

A is incorrect because in a negative ion the number of electrons should be more than the number of protons

C is incorrect because the numbers of neutrons and electrons are incorrect

D is incorrect because oxygen has 8 neutrons and hydrogen has 0

(1)

Question

number

Answer Mark

2

The only correct answer is B (28.2)

A is incorrect because this is the mass number of the most abundant isotope

C is incorrect because this is the average of the mass numbers without considering their abundances

D is incorrect because the percentages have been mixed up

(1)

Question

number

Answer Mark

3

The only correct answer is D

A is incorrect because the 1s and 2s electrons should be paired

B is incorrect because the 2s electrons should be paired

C is incorrect because the 2p electrons should not be paired

(1)

Question

number

Answer Mark

4

The only correct answer is D (3p subshell 6, third quantum shell 18)

A is incorrect because 2 is the number of electrons in a 3p orbital and the 3d electrons have been omitted from the

third quantum shell

B is incorrect because 2 is the number of electrons in a 3p orbital

C is incorrect because the 3d electrons have been omitted from the third quantum shell

(1)

Question

number

Answer Mark

5 The only correct answer is B (Group 3)

A is incorrect because the biggest jump is after the third ionisation energy not after the second

C is incorrect because the biggest jump is not after the fourth ionisation energy

D is incorrect because the biggest jump is not after the fifth ionisation energy

(1)

Question

number

Answer Mark

6

The only correct answer is D (1000)

A is incorrect because this is less than the first ionisation energy of sodium and phosphorus has 4 more protons

B is incorrect because this is less than the first ionisation energy of aluminium and phosphorus has 2 more protons

C is incorrect because this is less than the first ionisation energy of silicon and phosphorus has 1 more proton

(1)

Question

number

Answer Mark

7

The only correct answer is D

A is incorrect because magnesium chloride has ionic bonding

B is incorrect because magnesium chloride has ionic bonding

C is incorrect because the charges are incorrect

(1)

Question

number

Answer Mark

8

The only correct answer is C (ions and delocalised electrons)

A is incorrect because this is ionic bonding

B is incorrect because atoms do not attract delocalised electrons

D is incorrect because this is covalent bonding

(1)

Question

number

Answer Mark

9

The only correct answer is C (more protons than N3− but the same number of electrons as N3− )

A is incorrect because Al3+ has more protons and the same number of electrons as N3−

B is incorrect because Al3+ has the same number of electrons as N3−

D is incorrect because Al3+ has more protons and the same number of electrons as N3−

(1)

Question

number

Answer Mark

10

The only correct answer is B (Mg2+)

A is incorrect because anions are polarised and do not cause polarisation

C is incorrect because Na+ has less polarising ability than Mg2+ as it has a larger radius and a lower charge

D is incorrect because anions are polarised and do not cause polarisation

(1)

Question

number

Answer Mark

11

The only correct answer is C (ICl4−)

A is incorrect because CCl4 is tetrahedral

B is incorrect because CH4 is tetrahedral

D is incorrect because NH4+ is tetrahedral

(1)

Question

number

Answer Mark

12

The only correct answer is D (general formula)

A is incorrect because boiling temperature increases as the number of carbon atoms increases

B is incorrect because density increases as the number of carbon atoms increases

C is incorrect because the alkanes have different empirical formulae

(1)

Question

number

Answer Mark

13

The only correct answer is A (accepts a pair of electrons)

B is incorrect because electrophiles never have a negative charge

C is incorrect because not all electrophiles have a positive charge

D is incorrect because nucleophiles donate a pair of electrons

(1)

Question

number

Answer Mark

14

The only correct answer is B (5)

A is incorrect because there are 5 structural isomers – hexane, 2-methylpentane, 3-methylpentane, 2,2-

dimethylbutane and 2,3-dimethylbutane

C is incorrect because there are 5 structural isomers

D is incorrect because there are 5 structural isomers

(1)

Question

number

Answer

Mark

15

The only correct answer is A (E-2-chlorobut-2-ene)

B is incorrect because the two highest priority groups are opposite to each other

C is incorrect because chlorine is on the second carbon atom

D is incorrect because chlorine is on the second carbon atom and the two highest priority groups are opposite to each

other

(1)

Question

number

Answer

Mark

16

The only correct answer is C (bonds broken σ and π, bonds made σ only)

A is incorrect because a π bond also breaks in ethene and only σ bonds are made

B is incorrect because a σ bond also breaks in hydrogen

D is incorrect because only σ bonds are made

(1)

Question

number

Answer Mark

17

The only correct answer is A (Ca + 2HNO3 → Ca(NO3)2 + H2)

B is incorrect because the formulae of nitric acid and calcium nitrate are incorrect

C is incorrect because the formula of nitric acid is incorrect

D is incorrect because the formula of calcium nitrate is incorrect

(1)

Question

number

Answer

Mark

18

The only correct answer is B (0.424 g)

A is incorrect because this is the answer using a molar mass of 83 g mol−1 from NaCO3

C is incorrect because this is the answer just using the volume and a concentration of 1 mol dm-3

D is incorrect because this is the answer just using the concentration and not the volume

(1)

Question

number

Answer Mark

19

The only correct answer is A (6.0 x 10−2 g)

B is incorrect because 12 x 10−6 has been multiplied by 5 instead of 5000

C is incorrect because 12 x 10−6 has been divided by 5 instead of multiplied by 5000

D is incorrect because 12 x 10−6 has been divided by 5000 instead of multiplied

(1)

Question

number

Answer Mark

20

The only correct answer is A (0.36 dm3)

B is incorrect because the 2:1 mole ratio has not been used

C is incorrect because the mole ratio has been used as 1:2 instead of 2:1

D is incorrect because the mass has not been converted to moles

(1)

Section B

Question

number

Answer Additional guidance Mark

21(a)(i) An answer that makes reference to the following:

Heptane / petrol containing heptane:

burns less efficiently / smoothly

(than branched chains / cycloalkanes)

or

does not combust efficiently

or

causes pre-ignition / knocking

Allow burns for combusts and vice versa

Allow reverse argument e.g. petrol burns

more efficiently with no / small amount of

heptane

Allow the octane number would be low /

zero

Ignore:

It does not ignite / burn easily

It is difficult / harder to combust

Just ‘less efficient’ without reference to

combustion

Incomplete combustion

Amount of CO2 produced

Causes auto-ignition

References to toxicity and flammability

(1)

Question

Number Answer Additional guidance Mark

21(a)(ii)

Ignore bond lengths and bond angles

Ignore structural or displayed formulae as

working

Ignore skeletal formula with any CH3 groups

specified

(1)

Question

number


21(a)(iii)

correct equation

Example of equation:

C7H16 → C7H14 + H2

Allow multiples

Ignore any other type of formulae

(1)

Question

number


21(a)(iv)

An explanation that makes reference to the following points:

(oxides of nitrogen / these compounds)

dissolve in / react with / combine with / mix

with water (1)

(to form nitric / nitrous)

acid(s) / acidic solution / acid rain (1)

Ignore any reference to oxides of sulfur / sulfur

dioxide / sulfuric acid in answer

Allow moisture / rain / clouds for water

Ignore react with air / oxygen

Allow decreases pH of solution / rain

(2)

Question

number


21(b)(i) initiation (step /

reaction)

Allow initiating (step)

Ignore free radical / homolytic / chain / initial

(step)

Do not award heterolytic

(1)

Question

number


21(b)(ii)

C7H16 + Cl• → C7H15• + HCl

C7H15• + Cl2 → C7H15Cl + Cl•

(1)

(1)

Allow propagation steps in either order

Allow • anywhere on correct species

Ignore curly arrows, even if incorrect

Do not award • on species that are not

radicals

Penalise omission of • or incorrect number

of hydrogens in heptane once only in b(ii),

b(iii) and b(iv)

(2)

Question

number


21(b)(iii)

C7H15• + C7H15• → C14H30

TE on alkyl radical in (b)(ii)

Do not award product written as 2C7H15 /

C7H15C7H15

(1)

Question

number


21(b)(iv)


chlorine(free) radical / atom / Cl• removes another hydrogen

(atom in the product / chloroheptane ) (1)

(this free) radical reacts with another chlorine molecule / Cl2 (to

form dichloroheptane)

or

(this free) radical reacts with a chlorine radical / atom / Cl• (to

form dichloroheptane) (1)

TE on alkyl radical in (b)(ii)

Allow

C7H15Cl + Cl• → C7H14Cl• + HCl

Ignore Cl• substitutes a H atom

Allow

C7H14Cl• + Cl2 → C7H14Cl2 + Cl•

or

C7H14Cl• + Cl• → C7H14Cl2

Ignore just ‘further substitution’

Ignore

C7H16 + 2Cl2 → C7H14Cl2 + 2HCl

Any answer that shows 2Cl substituted

in one step

(2)

(Total for Question 21 = 11 marks)

Question

number


22(a)(i)

two correct values

(6) (53 268) 4.73

(7) (64 362) 4.81

Both numbers correct and must be to 2 d.p.

(1)

Question

number


22(a)(ii)

axes correct way round

and

linear scale and

points covering at least half the grid horizontally

(1)

both axes labelled (1)

points plotted correctly (1)

Example of graph:

Allow

Labels:

Allow log(IE / kJ mol−1)

Do not award log(IE) / kJ mol−1

Points:

TE on values in table for 6th and 7th log(IE)

Allow ±1 small square

Allow points joined by lines / bar chart

Ignore lines drawn from x axis to each point

Do not award a best fit straight line

Do not award lines joined to the origin

(3)

Question

number


22(a)(iii)

An answer that makes reference to the following:

the range of numbers / 1402 to 64362 is too large (to fit

on a graph / axis)

or

logarithms make it easier to plot the numbers

Allow:

A (very) long y axis would be needed (Some of)

the numbers are too large

The difference between the ionisation energies is

too large

So the numbers will fit on the graph

Allow logs give smaller (range of) numbers

(1)

Question

number


22(a)(iv)

An explanation that makes reference to the following

points:

the (large) jump (between ionisations 5 and 6) shows

the start of a new (quantum) shell (1)

there are two electrons that are harder to remove

and they are closer to the nucleus (1)

there are five electrons that are easier to remove and

they are further from the nucleus

(1)

Penalise use of orbitals instead of shells once only

Allow any answer relating the jump / large increase

to two (quantum) shells

Allow jump linked to 1s and 2s sub-shells

Do not award jump between incorrect numbers

Allow there are two electrons in the inner (quantum)

shell

Allow there are five electrons in the outer (quantum)

shell / five valence electrons

(3)

Question

number


22(a)(v)

An explanation that makes reference to the following

points:

Oxygen

oxygen (atom) loses a paired electron

(from a 2p orbital / 2p sub-shell)

or oxygen

electron is lost from a full (2p) orbital (1)

Nitrogen

nitrogen (atom) loses an electron from a singly-

occupied orbital

or nitrogen

loses an electron from a half-filled subshell

(1)

Repulsion

there is (more) repulsion between paired electrons

(than between electrons in different orbitals so less

energy is required to remove the electron in oxygen)

(1)

Penalise mention of incorrect orbital e.g. 3p once

only

Ignore any reference to nuclear charge / numbers of

protons / shielding / atomic radius

Allow M1 and M2 from diagrams showing electrons

in boxes

Allow oxygen has a pair of electrons in a (2)p orbital

or

there is spin pairing in oxygen in a (2)p orbital

Allow nitrogen has no paired electrons in the (2)p

sub-shell / (2)p orbitals

or

nitrogen only has 1 electron in each (2)p orbital / has

3 unpaired (2)p electrons / has a half-filled (2)p sub-

shell / has half-filled (2)p orbitals

Do not award just ‘nitrogen has a half-filled p orbital’

(3)

Question

number


22(b)(i)

dot-and-cross diagram Example of dot-and-cross diagram:

Allow overlapping circles

Allow all dots / all crosses

Allow dots and crosses in any order in the triple

bond

Allow the dots and crosses side-by-side in the triple

bond e.g.

x o

x o

x o

Allow the non-bonded electrons on each N shown

separately

Ignore inner shell electrons, even if incorrect

Ignore lines as bonds e.g.

x x x

o o o

(1)

Question

number


22(b)(ii)

calculation of moles of nitrogen atoms (1)

calculation of number of nitrogen atoms (1)

Example of calculation:

mol N2 = 5.60 = 0.20

28

and

mol N atoms = 0.20 x 2 = 0.40

or

5.60 = 0.40

14

number of N atoms = 0.40 x 6.02 x 1023

=2.408 x 1023 / 2.41 x 1023 /2.4 x 1023

TE on moles of nitrogen

Ignore SF except 1SF

Correct answer with no working scores (2)

(2)

Question number


22(b)(iii)

conversion of volume to m3 (1)

conversion of temperature to K (1)

rearrangement of ideal gas equation (1)

evaluation to give n (1)


volume of N2 = 108 = 1.08 x 10−4 m3

1 x 106

temperature = 25 + 273 = 298 K

n = pV RT

or n = 1.36 x 105 x 1.08 x 10−4

8.31 x 298 TE on volume and temperature

n = 5.9312 x 10−3 / 0.0059312 (mol)

Conditional on correctly rearranged equation in M3 Ignore SF except 1SF

Correct answer with no working scores full marks

(4)


Question

number


23(a)

CH2

Allow H2C

Ignore CnH2n / C4H8

Do not award C3H6

(1)

Question

number


23(b)

there are two hydrogens / both hydrogens on one of the

carbons (in C=C)

or

there are two / both methyl / CH3 groups on one of the

carbons (in C=C)

Allow there are two identical (functional)

groups / atoms on each carbon (in C=C)

Allow there is not CH3 and H on each carbon (in

C=C)

Allow there are not 2 different (functional)

groups / atoms on each carbon (in C=C)

Do not award two identical groups on the top /

bottom of the double bond

Do not award molecule or radical for

((functional) groups / atoms

(1)

Question

number


23(c)

dipole on bromine molecule

and

final product (1)

curly arrow from C=C to Br

and

curly arrow from Br-Br to, or just beyond, Br

(1)

intermediate (1)

lone pair on Br−

and

curly arrow from lone pair to positive charge

(1)

Example of mechanism:

Allow intermediate with positive charge on other carbon atom

Allow full marks for using formula 2 / any combination of

structural and displayed formula

Penalise half arrow heads once only

Do not award δ+ on intermediate in M3

Do not award δ- on Br in M4

(4)

Question

number


23(d)(i)

skeletal formula

Example of skeletal formula:


Do not allow O-H-C horizontally

(1)

Question

number


23(d)(ii)

(From)purple (to) colourless

Both colours needed for the mark

Allow pink or violet for purple

Ignore clear

(1)

Question

number


23(d)(iii)

hydrogen bromide / HBr

Ignore state symbols (g) / (l) / (aq) / (s)

Do not award bromine

(1)

Question

number


23(d)(iv)


(2-bromo-2-methylpropane is formed from a)

tertiary carbocation / tertiary intermediate (1)

(tertiary carbocation / intermediate)

is more stable than primary (carbocation)

or

a tertiary carbocation is the most stable (1)

Allow a description of a tertiary carbocation

Do not award secondary carbocation for M1

Allow primary carbocation is less stable than

tertiary

Allow secondary carbocation is more stable

than primary, if secondary carbocation

identified in M1

Ignore just ‘tertiary carbocation is more

stable’

Ignore any explanation of why one cation is

more stable than another

Ignore any reference to Markovnikov’s rule

Do not award tertiary product is more stable

(than primary)

(2)

Question

number


23(e)

4 carbon atoms linked by single bonds

and

both extension bonds (1)

rest of structure correct (1)

Example of repeat units:

Allow any combination of structural and displayed

formulae or skeletal formulae

Do not award 1, or more than 2, repeat units / 2

separate repeat units in M1

Penalise one or both extension bonds missing in M1

only

M2 is conditional on M1 or 1 or more than 2 repeat

units / 2 separate repeat units

Allow both methyl groups on carbons one and three or

two and three or one and four

Ignore any brackets and any ‘n’s or numbers


Ignore connectivity of CH3 groups

(2)

Question

number


23(f)

calculation / working of mol of alcohol (1)

calculation / working of mol of alkene if 58.2%

(1)

calculation / working of mass of alkene (1)

answer given to 2 or 3 SF (1)

Alternative method for M2 and M3

calculation / working of theoretical mass of

alkene (1)

calculation / working of actual mass of alkene

(1)


mol alcohol used = 6.85 = 0.092568 / 9.2568 x 10−2

74

mol alkene if 58.2% = 0.092568 x 58.2

100

= 0.053874 / 5.3874 x 10−2

TE on mol alcohol

mass alkene = 0.053874 x 56 = 3.017 (g)

TE on mol alkene

answer to 2 or 3 SF = 3.0 / 3.02 (g)

Conditional on working involving 74 and 56

Correct answer to 2 or 3SF with or without working scores

(4)

Alternative method for M2 and M3

mass alkene if 100% = 0.092568 x 56 = 5.1838 (g)

TE on mol alcohol

mass alkene if 58.2% = 5.1838 x 58.2 = 3.017 (g)

100

TE on theoretical mass

(4)


Question

number


24(a)


(l) is incorrect because the solutions are aqueous

or the

ions are (in the) aqueous (state) or

the state symbols should be (aq) instead of (l) (1)

silver ions should have one positive charge / Ag+

or

silver chloride is AgCl (1)

Allow silver nitrate and sodium chloride are

aqueous

Do not award if incorrect state symbol for

one of the species in the equation e.g. Ag is

(s) / AgCl is (aq)

Ignore just the charge on the silver ion is

incorrect / the formula of silver chloride is

incorrect

(2)

Question

number


24(b)

calculation of mol of C, H and Cl (1)

calculation of empirical formula (1)

calculation of molecular formula (1)


C : H : Cl

mol 3.09 : 0.26 : 9.15

12 1 35.5

= 0.2575 : 0.26 : 0.2577

(ratio 1 : 1 : 1)

Empirical formula is CHCl

molar mass CHCl = 12 + 1 + 35.5 = 48.5

molar mass (CHCl)n = 97 = 2

molar mass CHCl 48.5

Molecular formula is C2H2Cl2

Allow symbols in any order

Do not award 2CHCl

Ignore SF in mol and ratio

Correct molecular formula with some working scores (3)

Alternative method scores (3)

no. C atoms = 3.09 x 97 = 2 / 1.9982

12.5 x 12

no. H atoms = 0.26 x 97 = 2(.0176)

12.5 x 1

no. Cl atoms = 9.15 x 97 = 2

(3)

12.5 x 35.5

molecular formula is C2H2Cl2

Question

number


24(c)(i)

all 4 ion formulae (1)

all 4 (corresponding) m / z values (1)

Example of answer:

ions m / z

N(35Cl)3+ 119

N(35Cl)237Cl+ 121

N35Cl(37Cl)2+ 123

N(37Cl)3+ 125

Allow any other unambiguous way of representing

the formulae e.g. in words

Allow (1) for any two m / z values with

corresponding ion formulae

Ignore missing / incorrect charge on ion

Ignore mass number on N

Ignore bonds or + between Cl atoms / order of

atoms

e.g. N-35Cl-35Cl-35Cl

(2)

Question

number


24(c)(ii)

number of bonding pairs

and

number of lone pairs (1)

shape (1)

bond angle (1)

Example of table:

Number of bonding

pairs of electrons on

nitrogen

3

Number of lone pairs

on electrons on

nitrogen

1

Shape of molecule trigonal pyramidal

Bond angle 107o

Shape:

Allow 3-dimensional drawing e.g.

There must be at least 1 dotted/dashed line or

wedge for 3-d

Allow just ‘pyramidal’

Allow pyramid for pyramidal

Do not award tetrahedral

Bond angle:

Allow any number in the range 106-108o

Ignore missing °

(3)

Question

number


24(d)(i)

An explanation that makes reference to one of the following pairs

of points:

Polarisation route

an aluminium ion / cation is (very) small and highly charged

or

Al3+ has a small ionic radius / is small (1)

so it polarises / distorts the chloride ion / Cl− / anion (1)

Allow

Electronegativity route

there is a (relatively) small difference in electronegativity between

aluminium and chlorine (1)

so the electrons are (partially) shared (1)

Marks must come from the same route

– maximum 1 mark if one point from

one route and one point from the other

route

Allow the aluminium ion has a high

charge density

Allow a description of polarisation

Allow chlorine anion / ion

Ignore the aluminium chloride is

polarised

Ignore size of chloride ion

(2)

Question

number


24(d)(ii)

A description including the following points:

diagram showing two AlCl3 molecules joined through two chlorine

atoms (1)

dative (covalent) bonds

or

coordinate bonds (1)

Example of diagram:

Allow dot-and-cross diagram

Ignore missing arrow heads and lone

pairs from diagram

Do not award diagram with Al-Al / Cl-Cl

bond(s)

Allow dative covalent bonds labelled on

diagram / shown as arrows from Cl to

Al

Allow description of dative bonds

Allow M2 even if only 1 dative bond

shown / mentioned

Do not award M2 if dative bonds

starting from aluminium

Do not award M2 for any answer that

mentions ions / ionic bonds

(2)


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mark scheme (results) january 2019 - pmt

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